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Stock Compensation Plans and Other Employee Benefit Plans (Narrative) (Details) (USD $)
 12 Months Ended 3 Months Ended
Dec. 31, 2014
Rate
Dec. 31, 2013
Dec. 31, 2012
Mar. 31, 2015
May 31, 2012
May 31, 2011
May 31, 2009
Jan. 31, 2007
Dec. 31, 2011
Jan. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Additionally Authorized         300,000wtfc_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAdditionallyAuthorized          
Allocated Share-based Compensation Expense $ 10,100,000us-gaap_AllocatedShareBasedCompensationExpense $ 6,700,000us-gaap_AllocatedShareBasedCompensationExpense $ 9,100,000us-gaap_AllocatedShareBasedCompensationExpense              
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense 4,000,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 2,500,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense 3,300,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense              
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value $ 11.52us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue $ 17.49us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue $ 15.00us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue              
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value 2,300,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue 1,200,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue 5,400,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue              
Employee Service Share-based Compensation, Tax Benefit Realized from Exercise of Stock Options 900,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitRealizedFromExerciseOfStockOptions 485,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitRealizedFromExerciseOfStockOptions 2,100,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitRealizedFromExerciseOfStockOptions              
Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options 5,900,000us-gaap_EmployeeServiceShareBasedCompensationCashReceivedFromExerciseOfStockOptions 15,000,000us-gaap_EmployeeServiceShareBasedCompensationCashReceivedFromExerciseOfStockOptions 10,400,000us-gaap_EmployeeServiceShareBasedCompensationCashReceivedFromExerciseOfStockOptions              
Percentage Of Awards Paid In Performance Shares 17.00%wtfc_PercentageOfAwardsPaidInPerformanceShares                  
Maximum number of shares that could be issued based on the grants made to date 591,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber                  
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized 10,100,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized                  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value 7,800,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue 7,400,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue 6,400,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue              
Defined Contribution Plan, Employer Discretionary Contribution Amount 5,000,000us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount 4,900,000us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount 4,300,000us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount              
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent 90.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent                  
Stock Issued During Period, Shares, Employee Stock Purchase Plans 66,521us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans 62,096us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans 66,237us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans              
Employee Stock Purchase Plan, Compensation Expense 377,000wtfc_EmployeeStockPurchasePlanCompensationExpense 355,000wtfc_EmployeeStockPurchasePlanCompensationExpense 421,000wtfc_EmployeeStockPurchasePlanCompensationExpense              
Employee Stock Ownership Plan (ESOP), Number of Committed-to-be-Released Shares 15,008us-gaap_EmployeeStockOwnershipPlanESOPNumberOfCommittedToBeReleasedShares                  
Employee Stock Ownership Plan (ESOP), Shares in ESOP 192,499us-gaap_EmployeeStockOwnershipPlanESOPSharesInESOP                  
Two Thousand And Seven Plan [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized               500,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_AwardTypeAxis
= wtfc_TwoThousandAndSevenPlanMember		    
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Additionally Authorized           2,860,000wtfc_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAdditionallyAuthorized
/ us-gaap_AwardTypeAxis
= wtfc_TwoThousandAndSevenPlanMember		 325,000wtfc_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAdditionallyAuthorized
/ us-gaap_AwardTypeAxis
= wtfc_TwoThousandAndSevenPlanMember		      
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant 402,394us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_AwardTypeAxis
= wtfc_TwoThousandAndSevenPlanMember		                  
Ltip Awards [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period 3 years                  
Share Based Compensation By Share Based Payment Award Options Term 7 years                  
LTIP Performance-Based Stock Awards [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Deferred Compensation Arrangement with Individual, Compensation Expense 2,100,000us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense
/ us-gaap_AwardTypeAxis
= wtfc_LTIPPerformanceBasedStockAwardsMember		                  
Restricted Stock [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Maximum number of shares that could be issued based on the grants made to date 146,112us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		 181,522us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		 314,226us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		           336,709us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember		  
Performance Shares [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Maximum number of shares that could be issued based on the grants made to date 295,679us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		 307,512us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		 214,565us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		           100,220us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember		  
Minimum [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent 85.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		                  
Minimum [Member] | Two Thousand And Seven Plan [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period 3 years                  
Minimum [Member] | Ltip Awards [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Percentage Of Performance Based Award Payouts 0.00%wtfc_PercentageOfPerformanceBasedAwardPayouts
/ us-gaap_AwardTypeAxis
= wtfc_LtipAwardsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		                  
Minimum [Member] | Restricted Stock [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period 1 year                  
Maximum [Member] | Two Thousand And Seven Plan [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period 5 years                  
Share Based Compensation By Share Based Payment Award Options Term 7 years                  
Maximum [Member] | Nineteen Ninety Seven Plan [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Share Based Compensation By Share Based Payment Award Options Term 10 years                  
Maximum [Member] | Ltip Awards [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Percentage Of Performance Based Award Payouts 200.00%wtfc_PercentageOfPerformanceBasedAwardPayouts
/ us-gaap_AwardTypeAxis
= wtfc_LtipAwardsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		                  
Maximum [Member] | Restricted Stock [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period 5 years                  
HPK Financial Corporation [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Defined Benefit Plan, Number Of Participants     0wtfc_DefinedBenefitPlanNumberOfParticipants
/ us-gaap_BusinessAcquisitionAxis
= wtfc_HpkFinancialCorporationMember		              
Defined Benefit Plan, Benefit Obligation 6,400,000us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_BusinessAcquisitionAxis
= wtfc_HpkFinancialCorporationMember		                  
Defined Benefit Plan, Fair Value of Plan Assets 5,600,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_BusinessAcquisitionAxis
= wtfc_HpkFinancialCorporationMember		                  
Diamond                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Defined Benefit Plan, Number Of Participants   0wtfc_DefinedBenefitPlanNumberOfParticipants
/ us-gaap_BusinessAcquisitionAxis
= wtfc_DiamondBancorpIncMember		                
Defined Benefit Plan, Benefit Obligation 3,200,000us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_BusinessAcquisitionAxis
= wtfc_DiamondBancorpIncMember		                  
Defined Benefit Plan, Fair Value of Plan Assets 2,700,000us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_BusinessAcquisitionAxis
= wtfc_DiamondBancorpIncMember		                  
Two Thousand And Seven Plan [Member] | Restricted Stock [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense 254,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= wtfc_TwoThousandAndSevenPlanMember		 329,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= wtfc_TwoThousandAndSevenPlanMember		 15,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= wtfc_TwoThousandAndSevenPlanMember		              
Cash Incentive And Retention Plan [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Deferred Compensation Arrangement with Individual, Compensation Expense 20,000us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense
/ us-gaap_PlanNameAxis
= wtfc_CashIncentiveAndRetentionPlanMember		 115,000us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense
/ us-gaap_PlanNameAxis
= wtfc_CashIncentiveAndRetentionPlanMember		 357,000us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense
/ us-gaap_PlanNameAxis
= wtfc_CashIncentiveAndRetentionPlanMember		              
Deferred Compensation Arrangement with Individual, Distributions Paid   $ 0us-gaap_DeferredCompensationArrangementWithIndividualDistributionsPaid
/ us-gaap_PlanNameAxis
= wtfc_CashIncentiveAndRetentionPlanMember		 $ 1,200,000us-gaap_DeferredCompensationArrangementWithIndividualDistributionsPaid
/ us-gaap_PlanNameAxis
= wtfc_CashIncentiveAndRetentionPlanMember		             $ 473,000us-gaap_DeferredCompensationArrangementWithIndividualDistributionsPaid
/ us-gaap_PlanNameAxis
= wtfc_CashIncentiveAndRetentionPlanMember
Directors Deferred Fee And Stock Plan [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant 32,053us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_PlanNameAxis
= wtfc_DirectorsDeferredFeeAndStockPlanMember		                  
Deferred Compensation Arrangement with Individual, Shares Issued 19,488us-gaap_DeferredCompensationArrangementWithIndividualSharesIssued
/ us-gaap_PlanNameAxis
= wtfc_DirectorsDeferredFeeAndStockPlanMember		 30,547us-gaap_DeferredCompensationArrangementWithIndividualSharesIssued
/ us-gaap_PlanNameAxis
= wtfc_DirectorsDeferredFeeAndStockPlanMember		 22,220us-gaap_DeferredCompensationArrangementWithIndividualSharesIssued
/ us-gaap_PlanNameAxis
= wtfc_DirectorsDeferredFeeAndStockPlanMember		              
Deferred Compensation Arrangement with Individual, Common Stock Reserved for Future Issuance 266,264us-gaap_DeferredCompensationArrangementWithIndividualCommonStockReservedForFutureIssuance
/ us-gaap_PlanNameAxis
= wtfc_DirectorsDeferredFeeAndStockPlanMember		                  
Subsequent Event [Member]                    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent       95.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember